98 454 Mag Mpi mid range missfire
05-06-2019 | 08:26 PM
#1
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98 454 Mag Mpi mid range missfire
Alright I’ve been reading on this forum for a while trying to figure out this problem.
just bought the boat from original owner 360 hours well maintained.
says he had the dealer do bigger injectors and other work new.
Boat idles great as soon as you get it around 1,000 rpms you can hear it breaking up, hold it wide open and after about 45 seconds it takes off like a bandit up to 4,000 rpms won’t go over. If you hold it mid throttle it rolls coal like a freightliner!
i did plugs cap rotor
changed fuel separator.
checked codes on engine none just flashes 12, watched 4 sets of 12 flash 3 times.
Also boat is a 260 Velocity
any suggestions or help is appreciated.
just bought the boat from original owner 360 hours well maintained.
says he had the dealer do bigger injectors and other work new.
Boat idles great as soon as you get it around 1,000 rpms you can hear it breaking up, hold it wide open and after about 45 seconds it takes off like a bandit up to 4,000 rpms won’t go over. If you hold it mid throttle it rolls coal like a freightliner!
i did plugs cap rotor
changed fuel separator.
checked codes on engine none just flashes 12, watched 4 sets of 12 flash 3 times.
Also boat is a 260 Velocity
any suggestions or help is appreciated.
05-06-2019 | 11:15 PM
#4
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Posts: 9,594
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From: Ft. Worth TX
you can not just throw larger injectors nor any injectors at it and leave the stock ecm and other internals of the engine. What is your fuel pressure ? what ms pulse width thru out the rpm range is the injectors showing ? You need a scan tool for real diagnostics,
my guess it is the injectors and fuel pressure
So what injectors are installed and the rating of those injectors ?
You need to post your engine serial number as well. Later 1998 was the changing of the big blocks for ecm and a few other systems
my guess it is the injectors and fuel pressure
So what injectors are installed and the rating of those injectors ?
You need to post your engine serial number as well. Later 1998 was the changing of the big blocks for ecm and a few other systems
05-07-2019 | 06:06 AM
#6
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I didn’t see The Schrader Valve when peeking around yesterday did see the fuel cooler down by the port side engine mount. What type of scan tool do I need I have obd2 that goes to my laptop but nothing for obd1 or whatever these require. I’ll post serial number when I find it. He told me he had the dealer do the work so I assume the flashes the ecm accordingly along with required parts.
05-07-2019 | 06:09 AM
#7
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From: On A Dirt Floor
You need to find out exactly what was done.All Part #'s , reprogramming,and whom.
No assuming or you could be screwed.
Edit in: Did the engine used to have a Procharger or etc on it ?
No assuming or you could be screwed.
Edit in: Did the engine used to have a Procharger or etc on it ?
Last edited by SB; 05-07-2019 at 06:14 AM.
